Telephones typically have a single Boolean control for signaling the user's availability. This can be exemplified by a mobile/cellular phone. If the phone is turned-on, then the user is considered available. If the phone is turned-off, then the user is considered not available. Similarly PBX (private branch exchange) extensions have a ‘Do-Not-Disturb’ or ‘Send-All-Calls’ state to ensure either all incoming calls are received or all incoming calls are not presented.
The only control available to a telephone user today for them to choose whether they are interrupted by phone calls operates on all calls unselectively. If a user makes himself available, e.g. switches on a mobile phone, or programs their handset to clear any do-not-disturb state, then any and all calls placed to their extension will ring the phone.
After the call is established, and placed to their phone, the calling party information may be supplied to the called party, e.g. on the phone display. The called user can then elect to ignore the call, or even explicitly manually redirect it.
The disadvantage of this technique is that the operation:                a) causes an interruption to the called user, and        b) results in specific feedback to the caller, possibly allowing them to tell that their call was rejected and hence risking causing offence.        
The problem with this technique is made worse when the billing implications of some mobile phone networks are considered. For instance a GSM phone which is enabled for ‘roaming’ incurs charges for inbound calls (while roaming). A phone user may only want to incur these charges for certain calls (from certain callers).
It is an aim of the invention to provide an improved technique which addresses one or more of the above described problems.